608930 - slowdown playing youtube video in fennec

Status: NEW

(Core :: Layout, defect)

Description

[Timothy Nikkel (:tnikkel)]

Sudarsana Nagineni reported this issue in bug 604969 and we debugged this issue to figure out what was going on.

In bug 599113 we had to invalidate contents of layers that are currently scrolled out of view if their contents change so they have the correct contents when they are scrolled back into view.

Fennec uses the root scroll frame differently from Firefox in that it doesn't change the scroll position. So we end up determining that invalidate rects are (at least partially) scrolled out of view and we issue an extra thebes layers only invalidate for these parts where we didn't before bug 599113.

We need to figure out how to handle this properly for Fennec so we don't make useless invalidate calls.

Comment 1

[Chris Jones [:cjones] inactive; ni?/f?/r? if you need me]

The platform APIs fennec uses were designed with the expectation that fennec's frontend would change the scroll position.  If the underlying problem here (which I don't understand yet) were to go away if fennec's frontend did that instead of what it does currently, I would be tempted to re-classify this bug as Product:Fennec.  We don't need to work around our own code.

Comment 2

[Timothy Nikkel (:tnikkel)]

Firefox drops invalidates that come through scroll frames for areas that are currently scrolled out of view. With retained layers this is no longer a valid optimization because we may have retained content that is currently scrolled out of view: it needs to be invalidated so it is correct when it is scrolled into view. If the scroll frame doesn't have any idea of what is actually visible this logic makes no sense.

I don't care how we classify this bug, just as long as we fix it suitably :).